Compartment syndrome is a common condition where a traumatic or crushing injury causes muscle swelling, raising the tissue pressure in one of the body's compartments, such as an arm, leg or other enclosed space within the body. The increased tissue pressure begins a cycle in which the circulation is impaired, leading to higher pressures, which further decrease circulation, perpetuating the cycle. If the cycle is not treated by a fasciotomy (in which a large incision is used to relieve pressure in the extremity), it can lead to muscle death and catastrophic loss of function.
The fascia envelope that surrounds muscle and bone is strong and relatively inelastic. Because of the strength and inelasticity of the fascia envelope, the pressure inside the compartment may significantly increase with even a small amount of bleeding into the compartment or with swelling of the muscles within the compartment. Common causes of compartment syndrome include tibial or forearm fractures, ischemic reperfusion following injury, hemorrhage, vascular puncture, intravenous drug injection, casts, prolonged limb compression, crush injuries and burns.
The clinical signs of compartment syndrome are the 5 “Ps”: pain (out of proportion to the injury), paresthesias (numbness), paralysis (loss of muscle contractility), pallor (loss of pulses), tense skin and vascular congestion. Poikilothermia (loss of normal thermoregulation) can also be a symptom of compartment syndrome. The clinical presentation may be ambiguous and these signs cannot be assessed in an obtunded or unconscious patient.
Because the clinical signs can be confusing or ambiguous, particularly in early stages, compartment pressures are usually measured in order to confirm the diagnosis. Markedly elevated pressures are clearly indicative of compartment syndrome. Typically, the normal pressure inside the compartment is in the range of about 5-10 mm Hg. In cases where the compartment pressure increases to 50-60 mm Hg, there will almost certainly be tissue necrosis within the compartment due to lack of new blood perfusion. In this case, compartment release surgery (e.g., a fasciotomy) is necessary to avoid muscle death and potential catastrophic loss of function to the injured limb. This surgery involves a large incision to relieve the pressure in the injured limb and can be disfiguring. In some cases, a skin graft is required to close the incision. In addition, severe complications, including post-surgical infections, can occur. However, the risks associated with these complications are less severe than the complications associated with compartment syndrome.
There is some ambiguity and even disagreement as to what constitutes a dangerous compartment pressure reading. Some advocate a relative criterion in which the pressure is within 30 mm Hg of the diastolic blood pressure. Others recommend an absolute pressure but again there is some disagreement over whether that number should be in the high 20 mm Hg range or whether it should be higher in the mid-30 mm Hg range.
If the pressures clearly exceed the threshold, then a fasciotomy should be performed, but the challenge is whether to perform the fasciotomy when the pressure is just below the threshold (e.g., 20-25 mm Hg) and the patient only exhibits some (but not all) of the clinical signs (e.g. pain with passive extension, weakness, paralysis, or numbness). If the pressure measurement is repeated some time (e.g., 1 hour) later with no change in results, then the patient may be considered at borderline risk of compartment syndrome. Presently, the risks of compartment syndrome far outweigh the risks of fasciotomy. This leads to fasciotomies being performed that probably would not be necessary if there were a more reliable test. Fasciotomies can be disfiguring (i.e., long incisions requiring skin grafts to close) and accompanied by severe complications (e.g., infection), but the complications of fasciotomies are less severe than the complications of compartment syndrome. With more accurate information from stimulation, it may be possible to protect the at risk muscle by performing an endoscopic or minimally invasive fasciotomy without the need for a large incision.